Magnum round has a normal bullet that sets inside the case. LR and lesser use a heeled bullet which has the same od as the case. Thus, the magnum cyl has the step in it.....
SP is old school snub nose CC weapon. LCR is new school CC weapon sameo-sameo...... the .22 rf version is meant as a trainer for the full-size version, or as a CC for a person unable to handle the full-size version.....
The depression in the side of the bolt, that is visible and ACCESSIBLE from the ejection port, works quite well to assist the bolt into battery when needed....